Hugo de Lasa

Catalytic cracking kinetics in a novel riser simulator

Abstract A 45 mL bench-scale internal recycle reactor, named a “Riser Simulator” was used to crack a commercial FCC feedstock as well as pure compound mixtures on Octacat and GX-30 catalyst under short reaction times (3 – 10 s). The kinetic constants, related to an eight-lump model, were calculated based on a reactor model which intrinsically includes the effect of molar expansion during cracking. As well, the model takes into account feedstock composition since the gas oil feed is lumped into paraffins, naphthenes and aromatics in both heavy and light fractions. The Riser Simulator is well suited for representing short riser cracking reactions allowing the use of a wide range of conditions thus making it a valuable tool for determination of relevant kinetic data.

Conversion of syngas to liquid hydrocarbons over a two-component (Cr2O3-ZnO and ZSM-5 zeolite) catalyst : Kinetic modelling and catalyst deactivation

Abstract The present study describes the kinetics of syngas transformation into liquid hydrocarbons (boiling point in the gasoline range) using as catalyst a mixture of a metallic component, Cr 2 O 3 –ZnO, and of an acidic component, ZSM-5 zeolite. Experimental results were obtained in an isothermal fixed-bed integral reactor. The validity of several kinetic models, available for methanol synthesis, is analysed and modifications are proposed. These changes involve a rate equation with a CO 2 concentration-dependent term. Catalyst deactivation is also evaluated and the effect of the operating conditions on coke deposition is established. Moreover, the rate of CO conversion and the change of catalytic activity with time-on-stream were described using a kinetic model showing a weak influence of temperature.

Effect of the operating conditions on the conversion of syngas into liquid hydrocarbons over a Cr2O3–ZnO/ZSM5 bifunctional catalyst

The effect of the operating conditions (pressure, temperature, space time, CO/H2 ratio in the feed and time on stream) on the conversion of syngas into liquid hydrocarbons over a Cr2O3–ZnO/ZSM5 bifunctional catalyst has been studied by means of experimentation in an integral fixed bed reactor. On the basis of the results, the global stoichiometry of the process is established and the relative importance of the operating variables in order to reach a good compromise between catalyst activity and gasoline quality is analysed.

Modeling a Silicon CVD Spouted Bed Pilot Plant Reactor

This study reports a comprehensive multiphase gas-solid dynamic mathematical model that successfully describes the batch growth of silicon particles in a CVD submerged spouted bed reactor. This multiphase reactor model takes into account the hydrodynamics and interphase mass exchange between the different fluidized bed regions (spout or grid zone, bubbles and emulsion phase) and uses applicable kinetic rate models to describe both heterogeneous and homogeneous reactions. The model also incorporates a population balance equation representing particle growth and agglomeration.The CVD submerged spouted bed reactor operation is simulated by means of a sequential modular procedure, which involves the solution of the reactor model and the population balance equation.It is shown that the proposed CVD multiphase reactor model successfully simulates experimental data obtained from batch operation in a pilot scale reactor at REC Silicon Inc. The modeling of experiments obtained for different operating conditions allows correlating the scavenging factor as a function of the silane concentration for short- and long-term operations.

Modeling Fluid Catalytic Cracking in a Novel CREC Riser Simulator: Adsorption Parameters under Reaction Conditions

The complexity of a heavy gas oil feedstock and the multitude of reaction pathways have limited previous attempts to model fluid catalytic cracking (FCC). The demand for more detailed kinetic information motivates the use of pure components to first elucidate the dominant pathways and mechanisms and then determine the associated rate parameters, including adsorption constants and heats of adsorption. The aim of the present work is to evaluate adsorption constants and heats of adsorption, under FCC relevant reaction conditions. The experiments are carried out in a novel CREC Riser Simulator (batch reactor unit) using USY zeolite catalysts with different crystallite sizes (0.4 and 0.9 microns). This study confirms a special feature of the CREC Riser Simulator, as a valuable tool for the study of adsorption phenomena. Adsorption constants and heats of adsorption are evaluated for benzene, toluene, xylene and trimethylbenzene, at initial reaction conditions. Catalytic conversion experiments for 1,2,4-trimethylbenzene help to demonstrate the consistency of the determined adsorption parameters at various temperatures and reaction times. In addition, adsorption constants and heats of adsorption are found to be constant throughout the reaction time and the formation of coke does not hinder the adsorption of 1,2,4-TMB, although it significantly affects the reactivity of this model compound.

The CREC Fluidized Riser Simulator. Characterization of Mixing Patterns

The CREC Riser Simulator Reactor is a new laboratory scale unit that was invented at CREC-UWO (de Lasa, 1991). It was specially designed for catalyst testing and kinetic modeling under the conditions of riser and downer reactors. Preliminary work on mixing patterns in the Riser Simulator was already effected by our group using a helium tracer and a constant temperature hot wire anemometer (Pekediz et al, 1993) with both of these devices placed in the outer reactor annulus. However and given the possible ambiguity of the mixing patterns established with these data, helium tracer was injected in the present study into the central catalyst basket, while velocity measurements were effected in the outer annulus. This methodology allowed the definition of effective gas mixing time and gas superficial velocities at various reactor pressures and impeller speeds with increased confidence. This study found that gas mixing times corresponding to high gas recirculation rates in a CREC Riser Simulator occur over impeller rotational speeds ranging from 3000-6000 rpm and total reactor pressures ranging from 1-5 atm. With this end, gas mixing patterns in a Riser Simulator represent a well mixed unit, and thus, the importance of the Riser Simulator can be realized in the context of its potential use for gas-solid reaction kinetics.

Novel Photocatalytic Reactors for Water and Air Treatment

The development of water and air treatment systems based on heterogeneous photocatalysis is an area of major technical importance (Blanco and Malato, 1993; Matthews, 1993; Ollis et al., 1989; Pelizzetti et al., 1992). Harada et al., (1999) have stated, “... the design of highly efficient photocatalytic systems is of vital interest and one of the most desirable yet challenging goals in the research of environmentally friendly catalysts”. There is general agreement that an important obstacle in the development of highly efficient photocatalytic reactors is the establishment of effective reactor designs for intermediate and large-scale use, as demanded by industrial and commercial applications. To achieve a successful commercial implementation, several reactor design parameters must be optimized, such as the photoreactor geometry, the type of photocatalyst and the utilization of radiated energy. A fundamental issue regarding the successful implementation of photocatalytic reactors is the transmission of irradiation in a highly scattering and absorbing medium composed of water and fine TiO2 particles.

Catalytic Cracking of Plastic Pyrolysis Waxes with Vacuum Gasoil: Effect of HZSM-5 Zeolite in the FCC Catalyst

Catalytic cracking of waste plastics is an interesting option for selectively recovering raw materials or for obtaining fuels. In this paper, a new recycling strategy is proposed, which consists of upgrading the waxes obtained by flash pyrolysis of polyolefins in a FCC (Fluidized Catalytic Cracking) unit. The waxes have been obtained by flash pyrolysis of polypropylene at 500 ºC and they have been dissolved (20 wt% wax) in the vacuum gasoil (VGO) of a FCC unit. The runs have been carried out in a CREC-UWO Riser Simulator Reactor (atmospheric pressure; 500-550 ºC; C/O = 5.5; contact times, 3-12 s). A commercial catalyst and a hybrid one (containing HZSM-5 zeolite) have been used. The cracking of the mixture leads to higher yield of gasoline than in the cracking of VGO with a higher content of olefins. The results of the effect of the operating conditions (temperature and contact time) are qualitatively similar to those corresponding to standard feed. Consequently, no difficulties inherent to the presence of waxes in the feed are expected in the treatment of mixtures at industrial conditions. The presence of HZSM-5 zeolite in the catalyst causes a significant increase in the amount of LPG (especially C3-C4 olefins), at the expense of a decrease in the gasoline fraction, whose RON is 1-2 points higher than that corresponding to the commercial catalyst. The gasoline obtained also has a higher content of olefins (especially C5-C7) and benzene at the expense of a decrease in the amount of C6-C10 i-paraffins.

Determination of Kinetic Parameter in a Unified Kinetic Model for the Photodegradation of Phenol by Using Nonlinear Regression and the Genetic Algorithm

Abstract This study reports the kinetic parameter estimation in the photocatalytic degradation of phenol over different TiO2 catalysts by using the Genetic Algorithm (GA) and nonlinear regression. Reaction networks are based on a previously reported unified kinetic model (UKM) of the Langmuir–Hinshelwood type. Nonlinear least-squares fitting and GA are used to find the values for the kinetic constants. The computed parameters were found to predict experimental data for phenol photodegradation at different levels of concentrations. It is shown that both methods render close values for the kinetic constants. This suggests that UKM approach gives the global minimum and as a result, this method provides good and objective parameter estimates with low to moderate cross-correlation among kinetic constants and acceptable 95% Confidence Intervals (CIs). Global optimization by using GA requires extensive computer times of up to 5 minutes. Least square fitting provides the same results with computer times of seconds only. It is then concluded that the UKM approach effectively avoids overparameterization by finding the global optimum when optimizing the kinetic constants.

Composition and quality of the gasoline obtained from syngas on Cr2O3-ZnO/ZSM5 catalysts

Abstract The kinetic equations for the formation of the lumps of the gasoline produced (C5 + fraction), paraffins (C5-C8), xylenes (o-xylene, m-xylene and p-xylene) and aromatics (benzene, toluene, C9-C11) in the transformation of syngas on Cr2O3-ZnO/ZSM5 bifunctional catalyst have been established as a function of the concentration of both reactants (CO and H2) and CO2 byproduct. The effect of the operating conditions on the RON and on the molecular weight of the gasoline has been studied by experimentation in an integral fixed bed reactor in the range between 10 and 50atm and between 300 and 425°C. The octane index increases with Cr/Zn atomic ratio of the Cr2O3-ZnO metallic function, with Si/Al ratio of the HZSM5 zeolite, with space time and with the CO/H2 molar ratio in the feed, in that order, whereas it passes through a maximum with pressure (at 20 atm) and with temperature (at 375°C). On the other hand, the molecular weight of the gasoline increases with the Cr/Zn atomic ratio, pressure, CO/H2 molar...